Multi-layer lubrication utilizing encapsulating coating



June 1965 D. E. ARMSTRONG ETAL 3,191,286

MULTI-LAYER LUBRICATION UTILIZING ENCAPSULATING COATING Filed June 12, 1961 2 Sheets-Sheet 1 INSIDE PERIPHERY TRIM LINE FIG.2

9O ELL Too SHORT OUTSIDE n u PERIPHERY TRIM LINE ,J

EXTENDED OUTSIDE PERIPHERY F IG. 3 l I FINISH LENGTI-LU l FIG.1 "3a. 5 ESTARTING LENGTH I F|G.5 l

EXTENDED OUTSIDE PERIPHERY FINISH LENGTH WITH TRIM ALLOWANCE/ OUTSIDE PERIPHERY 90 ELL WITH LUBE "B" FIG.4

INSIDE PERIPHERY INVENTORS BY Mum ATTORNEY June 1965 D. E. ARMSTRONG ETAL 3,191,286

MULTI-LAYER LUBRICATION UTILIZING ENGAPSULATING COATING Filed June 12, 1961 2 Sheets-Sheet 2- FIG.6

90 ELL WITH ENCAPSULATING RESIN FILM AND LUBRICATING COATING OUTSIDE PERIPHERY LUBRICATING ENCAPSULATING COATING RESIN FILM EXAMPLE: FORMED 90 ELL WITH COATINGS INTACT AND UNIFORM IN THICKNESS INVENTORS DAVID E ARMSTRONG GERALD P ROESER ATTORNEY United States Patent 3,191,286 MULTl-LAYER LUBRHCATION UTILIZTNG ENCAPSULATING COATING David E. Armstrong, Doylestown, and Gerald P. Roeser,

Lahaslta, Pa; said Armstrong assignor to Horace T.

Potts Company, Philadelphia, Pa, a corporation of Pennsylvania Filed June 12, 1961, Ser. No. 116,527 Claims. ((31. 29-424) This invention relates to a novel lubrication system for metal which is to be subjected to forming operations comprising applying a removable substantially nondestructible solid synthetic plastic filmhereinafter known as the encapsulating filmto said metal and applying a lubricant coatinghereinafter known as the lubricating surface m0difierto said resin film to facilitate forming the encapsulated metal against a hard metal die.

The problem to which conventional liquid and solid film lubricants are addressed is concerned with the operation of mechanical aids, e.g., farm machinery, railroad motive equipment, automobiles, aircraft, manufacturing machinery, etc. for the purpose of eliminating friction and wear in metal to metal contact and not to the forming of metals under metal flowing forces in a steel die. Lubricating research, especially in the automotive industry, has contributed to a remarkable increase in service life of automobiles and trucks and although the lubricating industry has developed multi-purpose lubricants of exceptional dependability under extremes of load, lubricants for the deforming of metals have not been developed to withstand the much higher extremes of load which is entailed by the cold pressurized flow of metal against harder metal.

Despite the fact that a natural outgrowth of the lubrication industry was to apply lubricants originally devel oped for the automotive industry for the design of forming presses and machines, these conventional automotive lubricants have not been satisfactory for deforming of metals. Specifically, liquid lubricants of the mineral oil type, synthetic lubricants such as the stable nonvolatile esters of organic and inorganic acids, the metal soaps, the silicone oils, the fluorocarbons, the titanium esters, the naturally occurring fats, oil, waxes and rosin oils, have each been found to be unsatisfactory for deforming of metal against metal in the cold, by reason of metal scoring and seizing even though these liquid lubricants have been beneficially used in thin films to reduce friction and wear between metal to metal rubbing and moving surfaces in automotive applications.

Solid film lubricants such as graphite, copper phthalocyanine, molybdenum disulfide, alkaline earth oxides and other polyvalent metal sulfides, and certain polymers such as triiiuorethylene polymers and tetrafluorethylene polymers have also been proposed for lubrication of metal to metal parts under extreme pressure conditions, but have also been found to be unsatisfactory for deforming of metal.

7 Although the lubricating system of the present invention has some superficial similarity to the solid film lubricants which are well known in the art, there are essential differences in the method employed and in the spe cific materials which are used.

The new concept of the present invention and its inherent simplicity are thus better understood by comparing the encapsulating principle of the present invention with conventional (unmodified) solid film lubricants. The invention employs as a critical feature thereof the new principle of reduced coefiicient of friction between metal to metal through interposition of a physically permanent plastic barrier between one metal surface being deformed and the other metal surface of the die or forming structure. The coefficient of friction is no longer that of lubricant between metal and contacting metal. Instead, it is the coelficient of friction between plastic capsule about the metal workpiece and the metal of the die. This coefficient of friction is not the inherent value of the plastic material of the capsule since it is necessary, in accordance with the invention, to reduce the coefiicient of friction between the plastic capsule and metal of the die to a value which permits the plastic material to remain dimensionally intact yet allows the underlying metal of the workpiece to flow under tensile forces which may be in excess of 100,000 pounds per square inch.

In accordance with the invention, a unique surface treatment of the encapsulating film is effected by treatment with a lubricating surface modifier (hereinafter called the modifier) having a melting point in the range of 37-1l0 C. and a lubricating action between the capsule and a steel die whereby an extremely low coelficient of friction is achieved. This permits successful use of the lubrication of the invention at room temperature for coldforming of metals.

The lubricating modifier is characterized chemically by its low coeificient of friction against plastic and metal, by its high degree of affinity for the base plastic material of the capsule due to the presence of highly polar nitrogen or oxygen atoms or both types of atoms in the molecule of the modifier and is characterized physically by its uniquely narrow melting range lying between about 37 C. and 110 C.

Examples of chemical species of modifier bearing polar nitrogen atoms and groups include fatty amines and nitriles substituted with long hydrocarbon radicals of melting point lying between 37 C. and 110 C., e.g., stearyl nitrile, nonadecylic nitrile, arachidyl nitrile and chlorinated and fluorinated derivatives of these nitriles within this melting range distearyl amine, arachidylamine and chlorinated and fiuorinated derivatives of these.

Examples of modifiers having melting point of 37 C.- 110 C. including both the polar and nitrogen group are the fatty amides and quaternary compounds substituted with fatty acid esters and preferably of polyamines and polyhydroxyamines. In the first category of fatty amide there may be used oleamide, ethylene stearamide, mixtures of oleamide and stearamide, hydroxy stearamide, mixtures of hydroxystearamide and stearamide. These fatty amides may be mixed with fatty amines, for example, mixtures of stearamide with oleyamide (primary amine) in proportions as will give a melting point above 37 C.

In the second category of quaternary ammonium compounds there may be used such compounds as fatty acid esters or wax esters of ethylene diamine shown in US. Patent No. 2,695,243 or of N,N,N',N'-tetra kis hydroxyethyl ethylene diamine as are shown in U.S. Patent Nos. 2,878,144 and 2,878,273.

The materials selected from these patents are those having a melting point above 37 C. and less than 110 C. indeed, at a melting point of less than C. these materials appear to operate more effectively.

Thus, in general it is seen that fatty nitrogen compounds, amides, amines, amine salts, nitriles and quaternary compounds in the melting point of 37/ C. are generally operative as the lubricating modifier.

The modifier is preferably a low melting amide of oleic acid, a low melting polyglycol, a low melting, self-emulsifying wax such as myristyl myristate, or a low melting, low-molecular weight linear polymer of ethylene o-r pro pylene, or equivalent low melting, low-molecular weight copolymer of ethylene and propylene. These materials are applied either as a solution or dispersion in a volatile of the strongest metals.

medium, such as water, or an organic solvent, or as melt.

As a result of this treatment, the surface of the solid encapsulating film is physically altered to exhibit a kinetic coefiicient of friction against a polished steel-forming sur a hot face of about 0.01-0.0Q and a static coefiicient of friction of substantially the same order.

The lubricated surface stratum which is achieved by this treatment to impart high lubricity and a coefiicient of friction lying between0.01 and 0.02 isextrernely thin and surprisingly may or, may not be a continuous coating. It has been discovered that the low melting lubricant, be it the low melting amide, or the low-molecular weight polyglycol, or thelovv-molecular weight ethylene polymer, when applied from dispersions form islands or particles, but that. under cold-forming pressure or atslightly elevated temperature, e.g., up toabou-t 100 C.,' either melts or softens to a very thin lubricating layer at the interface between the film encapsulated workpiece and the di e. Of course, these lubricants deposit continuous films when applied molten and said continuous films behave like the discontinuous films described above. a I I With the uniquely suit-able lubricant components of the present invention, there is found- .to exist a limited compatibility between the lubricating coating and the hard non-destructible underlying encapsulating resinous base so-that the lubricant stays'ou top of the film base. It

se as a lubricant there is applied a special coating, prefer 1 ably a separately formed surfacecf lubricating material which is capable of movement on the encapsulation film. I As a result, the film isconverted to a capsule-bearing lubricant surface by the specificmeans taught by the invention to. achieve a muchlower coefiicient of friction of plastic film against metal, e.g., steel, iron, copper,

titanium, zirconium, etc, than could be achieved by any known lubricant per se, liquid or solid, directly interposed between the two metal surfaces and beingused under the conditions of metal flow.

It is an advantage. of the invention that the lubricant solid encapsulating film and surface lubricant thereon are readily' dissolved i'n common-solventseither for coating has been discovered by trial and error that there mus-t be 7 no substantial penetration or softening of the plastic film by solvent carriers'for the surface modifying agent, or by the agent itself, since this would weaken the encapsulating film to permit tearing which would lead to scoring, then to metal to metal seizing and galling during cold-.

forming.

It has been discoveredjthat the encapsulating resin film must be substantially incompressible. Also a minimum adhesion shear strength of the solid lubricant-carrying film is needed to prevent separation from the underlying metal purposes or for removal purposes at room temperature. Such common organic solvents may be used. as chlorinated hydrocarbon solvents, solvent naphthtnamyl acetate, ethyl material which is thus protected during cold-forming; A

high value of modulus of elasticity t-eristic of the resin.

The minimum value of adhesion strength of is a desirable characthe encapsulating film to the base metal under cold-forming forces at least 2 kilograms per square millimeter, 'or at least 600 pounds .per square inch. 'Incompressibility,

adhesion, hardness and toughness in the film provide a non destructibIe capsule which is uniquely'suited for cold-. forming of metals under forces beyond the tensile limit The tensile strength of the tough encapsulating film material must be a minimum of 3000 pounds per square :inch, preferably. about 4500 pounds per square inch in order-to maintain the integrity of the plastic capsule under metal flow conditions. The

elasticity of the encapsulating film as measured by percent elongation must beat least 3 percent to prevent rupture during the forming operation. V I 7 Also the encapsulating film must have a hardness value acetate, ethylene glycol monomethyl ether, aromatic hydrocarbon solvents, mixtures of aromatic and high boiling aliphatic hydrocarbon solvents, and ketones such as acet0ne, methylethyl ketone, arnyl ketone, etc.

It is. a further advantage'of the invention that the formation of the solid polymer encapsulating film and surface lubricant onto the base surface does not need elevated temperatures to create adhesion thereto. Excellent adhesion is obtained by coating the base polymer from a solution or'a water dispersion and by air drying at room temperatures.

p In the article by W. E. Cambell'Lubrication Engineering, vol. 9,'pages 195-200 (1953), the following eight (8) physical'requirements for solid film lubricants are stated to be. necessary for eflicient lubrication to protect the surface of a metal against Wear, corrosion and thermal effects:

(1) Low shear strength (2) Strong adhesion to the surface of metal or other base V (3) Good elasticity (4) Continuity of film with self-healing characteristics to overcome breaks inthe film (5) High thermal stability of at least 20 Brinell in order to provide a substantially n-on-destmctible film for carrying the surface lubricant having a low coefiicient of friction against the metal die in order to preventrub-olf during the forming operation or wearing metal .parts. a Ohlorinated rubber is preferred as the encapsulating film materialwhich is to be subjected to surface modification for providing a low coefficient of friction againstmetal.

The encapsulating film thickness is readily controlled between /z to 3 mils in thickness. In the case of chlorinated rubber, this encapsulating film has a tensile strength of about 2500-5000 p.s.i., a modular of elasticity ofabout 140,000 pounds, and'elongation of up to about 4percent. v V I Other hard, strong, and metal-tenacious resins may also be used, such as certain vinyl polymers, e.g., a copolymer of 87%-95% vinyl chloride, l2%1 3% vinyl 6 High melting pointabove170 F.

(7) Good thermal conductivity (8) Chemical inertness tosprotect the parts from corrosion and freedom from abrasive filler or contaminants The present invention departs from the concepts expressed by Cambell above by first encapsulating the metal parts to be formed with a substantially non-destructible solid synthetic plastic encapsulating film to completely .protect'the metal from frictional contact with other metal. Secondly, the surface of the encapsulating film is coated with a lubricant modifier to further isolate the metal part being formed from the metal of the forming die. In other Words, a lubricated plastic bodythe encapsulated metal partis being formed in the metal forming die, not the metal partper se. This obviates the seizing and galling tendencies that Would be present if the metal part, unencapsulated, were formed directly in the metal die where metal to metal contact would exist. The, encapsulating film is 'a hard, tough, material having an extremely high shear strength, low elasticity, high'hardnesaand a high melting point.

t Accordingly, an entirely new concept is seen in comparison with the conventional solid film lubricant.

Thus, in accordance with the present concept of the invention, it is not possible to rely upon a single polymer species or such species with or without the usual plasticizersr, softeners, fillers, etc., to achieve adequate solid encapsulating film protection from cold-forn1ing metals under extreme pressures. This can be better understood if the properties of commercial polytetrafiuoroethylene, the best solid film coating of the prior art are briefly considered.

Tetrafluorethylene polymer, known by the trademark of Teflon (DuPont) which is the solid polymer of choice for lubricant properties is unsatisfactory per se as a solid encapsulating film for cold-forming of hard metals. Despite the low kinetic coeificient of friction of Teflon, e.g. 0.2-0.3 against polished hard steel, cold-working forces scour the Teflon off the surface upon which it has been coated so that the encapsulating film tears away from the underlying metal surface to cause scoring. This scouring action is possible because of the inherent softness and ease of deformation of the Teflon. Particularly noteworthy is the fact that the adhesive shear strength and hardness values of this tetrafiuorethylene polymer is so low as compared with a vinyl chloride polymer or chlorinated rubber encapsulating material used in accordance with the invention that rapid and complete failure occurs when it is used for cold-forming of hard metals or of soft metals having a tendency to seize against polished steel, polished chromiumm or polished cermets. Thus Teflon solid film is subject to seizing and galling in steel dies when used in the method and apparatus described in US. Patent No. 2,971,556, Armstrong et al., and Serial No. 24,829, Armstrong et al., now abandoned.

If a harder polymer like polyvinyl chloride is employed as an encapsulating film it fails because it is not adhesive enough and flakes off during the cold-forming operation. Hardness without adherence cannot withstand the high forces employed to cold-form hard metals.

Similarly, a waxier polymer such as high melting point (130 C.+) polyethylene used without surface modification, fails because its adhesion value is also too low and also because coeflicient of friction against polished steel is too high (0.33) for good lubrication.

These unfavorable values of coefiicient of friction of selected polymer against polished hard steel can be better understood if one views the characteristics of the physical behavior of plastics sliding on harder metal, e.g., harder than the plastic itself, under application of increasing compressive load normal to the plastic metal interface.

Ordinarily, when a plastic slides on harder metal, adhesion occurs between the dissimilar surfaces and shearing takes place within the plastic material itself, whereas if the plastic material slides on a softer metal, shearing occurs in the metal. It is when the adhesion between the surface of the plastic encapsulating film and the surface of metal is so small that shearing occurs at the plastic-metal interface that the value of coeflicient of friction can be satisfactory. However, this low value of encapsulating film adhesion cannot obviously Withstand tearing forces if it is intended that the film stick to the base metal.

In summary, the physical characteristics of the encap sulating film which have been discovered to be necessary in accordance with the invention are: (1) good hardness, (2) high tensile strength, (3) high film integrity (resistance to shear and creep), (4) good flexibility and (5) resistance to thinning by compression.

Such polymers as polystyrene are wholly unsuitable by reason of excessive brittleness and low impact resistance. These cause the encapsulating film to fracture under load. Polyvinyl acetate and high butyrate-containing cellulose aceto-butyrate encapsulating films are unsuitable because of excessive elongation and excessive cold flow.

Alcohol soluble nylon which is much more elastic than either of the suitable vinyl chloride-vinylidene chloride encapsulating polymers, or suitable vinyl chloride carboxylic acid copolymer or the preferred chlorinated rubber polymer of the invention is also unsuitable because of excessive elongation. The nylon base material has a high elongation and undergoes excessive cold flow. The high tensile strength of the nylon base polymer, about 4000-7000 p.s.i., and its excellent adhesion to metal do not compensate for its excessive elongation.

In a preferred embodiment of the invention using a hard chlorinated rubber (specific gravity 1.50-1.65 and containing about 67% chlorine) as the encapsulating material, excellent adhesion is achieved to an underlying cleaned body of stainless steel. The Brinnel hardness value of the chlorianted rubber capsule is about 2530. This hardness is not altered by modification with the preferred surface coating of oleamide under the application of metal flow cold-forming forces.

There is observed no change in the film dimensions. Neither film continuity nor thickness are altered under a cold-forming pressure of 100,000 p.s.i. or higher in the case where oleic acid amide is applied as a top coating over chlorinated rubber or as a modifier in a stratified coating admixed with chlorinated rubber.

Initially the surface coating of oleic acid amide is present at room temperature as a non-tacky discontinuous thin coating which is dry to the touch and which can be scraped off readily. However, the effective surface hardness is that of the main body of the film. Furthermore, when all the particles and islands are smoothed out during the cold-forming operation, the lubricant coating remains on top of the encapsulating resin base as a hard film, much harder than Teflon for example.

The chlorinated rubber encapsulating body may be first applied as a base film to the metal part and the oleic acid amide thereafter applied as a top coating or the chlori nated rubber and the oleic acid amide may be mixed in the original coating solvent for encapsulation and lubrication by a single application. By adjusting the solids concentration and controlling the solvent selection, a stratification of oleic acid amide over the encapsulating base resin is achieved, and the lubricant amide component effectively stratifies on the surface of the encapsulating film due to its difference in density and limited compatibility in the presence of organic solvent.

To illustrate stratifying mixtures there are prepared solvent solutions of chlorinated rubber and oleic acid amide in proportions by weight of 50/50, 33/66 and 10/90 at 25% solids in xylol. This solution deposited by brushing as a continuous film 2-3 mils thick on a degreased stainless steel tubular blank and after air drying results in Stratification with the amides separating as blotches and particles on the surface. The highly-adherent, hard, trough chlorinated rubber base stratum is oriented as a continuous solid encapsulating film about and at the metal interface. The soft oleic acid amide surface modifier stratum after thorough drying in suificiently thin layer separates as a discontinuous dry surface in the form of islands or particles. Thorough drying is necessary to prevent failure of the encapsulating film. Stratification occurs best at the proportions of 33/66 to 10/90.

The use of an organic solvent for depositing the lubricant coating on the solid encapsulating film base is not necessary and indeed, is not preferred in practice. It is preferred that there be used an aqueous volatile vehicle which does not soften the resin capsule. An oleamide emulsion works better than a solvent solution.

A low-molecular weight polymer in the form of an aqueous emulsion of linear polyethylene, molecular. weight 4004000 and melting point about 105 C. also works well. This latter emulsion or an aqueous solution of waxy polyethylene glycol or copolymer, molecular weight of UGO-20,000 can be used or can be blended with an organic solvent solution of chlorinated rubber or tially non-destructible solid encapsulating film of themvention is of medium to high molecular weight at a chlorine content of about 67% as evidenced by good solubility in aromatic hydrocarbons such as benzene, toluene or xylene (up to about 40%) total solids by weight of hy drocarbon solvent and of medium to low viscosity in said hydrocarbon solution. Satisfactory encapsulating films have been produced as shown in Example lwith chlorinated rubber having a specific viscosity value of 0.70

measured in dimethyl formamide solvent, 1 gram of chlorinated rubber per deciliter of diethyl formamide solvent. The viscosity and molecular weight are such as pointed out above as will deposit a film up to about 3 mils in thickness by dip coating at solids, in 'xylol solvent onto clean steel. The so-deposited. encapsulating film is non-inflammable, stable to ultra-violt light, extremely impermeable to water and highly resistant to attack by'alkali or acid. a

If the encapsulating film is plasticized with primary chemical plasticizers such as tricresyl phosphate or dibutyl phthalate or with such secondary plasticizers as lard oil,

8 hyde resin, urea formaldehyde resin and phenol formaldehyde resins in theamounts recommended and known for addition to these tripolymer resins available commercially under these trade names VAGH and VMCH from Union Carbide Company. When these heat-setting resins are added, the encapsulating films become thermoset by baking at elevated temperatures of 300-450; F. for 10-30 minutes without any substantialalteration of the necessary hardness, adhesion, elongation and tensile strength characteristics. y

In similar manner these same additions of Carbamide 'or phenolic resinfmay be employed to render thermoset I and a decorative function for long lasting coating.

t Thus the requirement in accordance with the invention for easy solubility in an-organic solvent holds for the case where clean bare formed metal is to be produced but when insoluble thermosetting polymer is used the finish can be 7 left on the formed form.

linseed oil, tung oil, etc. it is unsatisfactory because of softness and tends to tear away from the underlying metal causing seizing and galling.

If the molecular weight of the preferred chlorinated rubber encapsulating resin is too low, e.g., susbtantially less than specific viscosity value of 0.50 measured in di-.

methyl formamide, then the encapsulating film tends to flake off from the metal base and reproducible lubrication during metal forming without destruction of the capsule is not obtained.

If thespecific viscosity is too high, e.g., above 0.85, the solutions become excessively viscous to make it difficult to brush, spray, dip or cast the coating from organic I V solvent solution such as xylol.

This difiiculty is not encountered when chlorinated rubber encapsulating film is applied out of an aqueous dispersion (oil-in-Water type). The advantage of slightly higher encapsulating film thickness is desirable for some applications, improving rather than lessening lubricating efficiency with the special lubricant material of the invention applied to the film capsule. V

Obviously, the metal workpiece is carefully cleaned and dried before encapsulating. Where rough metal surfaces are encountered it may be desirable to use heavier encapsulating film thicknesses, e.g., in excess of 3 to 4 mils in order to provide a smooth and level outer encapsulating film surface. In any event, the thickness of the encapsulating film is always sufiicient to obliterate surface imperfections or roughness in the underlying metal.

The solvent for the encapsulating resin should be completely volatile on standing at room temperature to facilitate air drying. If high boiling oily solvent residues Thus, "it, will be appreciated that the lubricant encapsulating films of these vinyl polymer types are also useful where decorative protective finishes are desired. When the metal stock is designed to be finished, this may be done in accordance with the invention prior to fabricating, the thermoset coating fulfilling both protective and lubricating functions. As an example, lacquer-coated corrugated iron or aluminum sheet, metal siding for the home, decorative paneling, cans, pails and enclosures may be first coated and'then formed by cold-forming standard methods to provide a finished coated product.

Also ducting for air conditioningand heating, metal hardware, metal whe'els for automotive or farm equipment cold-stamped or cold-formed may be provided with the thermosetcoating. Obviously, any of these articles which are to be put in final form of bare shiny metal are used with the thermoplastic encapsulating film and the encapsulating film is removed. Either of these varieties, thermoplastic or thermoset, may be used for lubricating and/or finishing window framing. of aluminum, magnesium or steel, for "wire drawing and for temporary or permanent protection of die surfaces. The lubricant enuse as wet or as dry bearings may also be lubricated to good advantage. Leaf springsas are used in'trucks and remain after air drying, these soften the capsule and prevent attachment of the film to the base for coldforming the encapsulated metal in a die.

The capsule for the metal workpiece when formed of vinyl chloride-vinyl acetate-carboxylic acid copolymer has the obvious advantage overchlorinated rubber in being capable of being adapted tobe-thermosetunder the action of heat and thereby converted from a' softer,

fusible and solvent-soluble condition to a harder infusible and solvent-resistant condition. Carbamide resins and phenolic resins which are, heat convertible and compatible with vinyl chloride resins of the VMCH type and of the VAGH type may be mixed with said 'vinyl resin, for example, melamine formaldeautomobiles may be given a substantially indestructible solid encapsulating film lubricant coating to improve their performance. Similarly, rotating seals, stufiing boxes and packing glands for moving machine parts can be uniquely coated with a non-destructible coating and operate in a fashion as can entirely eliminate oil seals. By employing alfluid bed for the coated member of powdered amide, oil is entirely eliminated, dirt and foreign matter Which ordinarily are entrapped in liquid oil type I Q dry lubrication system .is achieved.

lubricants can be completely excluded and an essentially 9 EXAMPLE I To illustrate the extreme force conditions which the embodiment of organic solvent-soluble thermoplastic encapsulating film and lubricant modifier in accordance with the invention must withstand, this example describes the simultaneous cold-forming and cold-sizing of a 90 L of stainless steel, carried out by the method and the apparatus of copending application, Serial No. 24,829 filed May 13, 1960, now abandoned. This cold-forming opertaon is selected as a typical example of the application of the multi-layer lubrication of the present invention. Another method and apparatus which demonstraes the utility of the present invention is that disclosed and claimed in US. Patent No. 2,971,556, granted February 14, 1961, to Armstrong et al.

A beveled tubular blank of circular crosss-ection of stainless steel 6 /8 inches long length, 6% inches short length, .109 inch wall thickness and 2,375 inches outer diameter, is coated with an organic solvent-soluble thermoplastic encapsulating film by brushing onto the chemically cleaned metal base. The encapsulating film is applied as a lacquer consisting of a xylol solution of chorinated rubber (25% solids in solvent) in a single coat and a top coating of oleic acid amide (10% solids) in 1,1,1-trichloroethane is applied thereto and is identified as lubricant B in the accompanying drawings. The first coat is completely dry before the second coat of lubricant is applied. The base encapsulating coat is about 1 to 2 mils in thickness and the top lubricant coating, lube B in the drawings is about 1 mil thickness. The total encapsulating plastic film and lubricant thickness is about 2 to 3 mils. The upper stratum of high lubricity is formed in the top coating step as a discontinuous surface layer consisting of particles of oleic acid amide which, under high compressive forces at room temperature, becomes continuous.

The blank is then subjected to forming forces of 1,100 pounds and counterthrust forces of about 500-600 pounds in the apapratus of copending application Serial No. 24,829 and with a clearance of about 0007-0012 inch in the die.

Under the cold-forming forces the shorter length of 6% inches in the stainless steel is uniformly thickened by controlled metal fiow up to an increase in thickness of about 30% in the 10 of are at the maximum bend and then is decreased uniformly in thickness to the original thickness value in the following 5l0 of are at the maximum bend. The longer length is thinned by controlled metal flow to a value of about 5% less than original thickness at the maximum radius of bend, this slight thinning being gradual and continuous along the larger peripheral arc to merge into the unchanged area of stock having the original thickness. There is no measurable thinning of the composite solid film lubricant.

A second L was made in the same apparatus and using the identical encapsulating film of chlorinated rubber as in the first part of this example, but using conventional commercial, water-emulsified lard oil lubricant which is the recommended lubricant for tin shop cutting, punching and forming. The commercial lard oil lubricant is identified as lube A and the forming of the 90 L is described in detail below in comparison to the forming of the 90 L using oleamide lubricant coating, lube B, identified above. In this description which follows reference is made to the accompanying drawings in which:

FIG. 1 is a diagrammatic illustration of the starting length of straight tubular blank from which a 90 L in Example I herein is manufactured;

FIG. 2 is a diagrammatic illustration of a 90 L produced with lube A and found to be unsatisfactory by reason of insufiicient exterior length indicative of an excessively high coefficient of friction of lube A restricting metal flow during forming and causing a shorter overall length;

'FIG. 3 is a diagrammatic view illustrating a projection 10 of the outside periphery of the L of FIG. 2 of Example I for lube A;

FIG. 4 is a diagrammatic view illustrating the manufacture of a L using lube B in accordance with the invention and found to be satisfactory by reason of suflicient length, this additional length in comparison with FIGS. 2 and 3 being due to unrestricted metal flow during forming whereby sufficient excess metal resulted so that a finish cut was made possible to give the leading end of the formed L a square cut and a uniform length in relation to the trailing end of the fitting;

FIG. 5 is a diagrammatic view showing the projection of the outside periphery of the satisfactory 90 L of FIG. 4, Example I, using lube B in accordance with the invention; and

FIG. 6 is a diagrammatic view showing a cross section of a formed 90 L with coatings intact and uniform in thickness.

In accordance with the figures of the the drawing, there is clearly shown that the overall length of formed 90 LS can vary on the leading edge up to 11/32". The controlling factor of this variation in possible length is the coefiicient of friction of the lubricant used on the blank tubular piece.

It has been determined in the manufacture of a 2" 90 L that indentation in the workpiece may be caused by an excessive uneven coating of chlorinated rubber. Thus, ample proof is visually seen that the encapsulating film does not flow under forming pressures. From this actual demonstration the present novel principle of encapsulation of the metal by a plastic material is believed to be clearly demonstrated There was also made a 2" 90 L showing an indentation in the tubular workpiece caused by an excessive blob of oleamirle applied to the part of the tubular blank before forming. This again demonstrates the substantial non-compressibility of the lubricant of the invention.

From the foregoing example it will be seen that the adhesion, hardness, toughness, incompressibility and low elasticity of the chlorinated rubber film constituting the preferred solid base encapsulating stratum is sufiicient to permit the controlled fiow of hard metal such as stainless steel at room temperature under metal forming forces beyond the elastic limit of the metal, e.g., of the order of about 100,000 pounds per square inch without any measurable decrease in film thickness as a result of shear and any noticeable compressive deformation of the film and without any breaking of the film.

Once the film is broken away from the metal surface, the steel wearing surface of the die exposes the underlying base metal and causes harmful seizing, scoring and galling of the workpiece due exclusively to the failure of the solid film.

The critical nature of the satisfactory lubricant material for interposition between the resin capsule and the steel the is farther emphasized by other experiments made by the inventors herein to compare the satisfactory oleamide lubricant in Example I, the satisfactory low molecular weight polyethylene emulsion lubricant of Example II below and the chlorowax 40 lubricant of Example III below with the following lubricant coatings found to be unsatisfactory in the same manner as lard oil, lube A, by the test of Example I and reference made to the drawing for the physical results.

Instead of an organic solvent solution of oleic acid amide, e.g., 10% solids in 1,1,1-trich1oroethane, there may be applied oleic acid amide emulsified in water as the top coating. This water emulsion is preferred for application to the organic solvent solution since the latter tends to leave residual solvent which must be driven off by thorough drying and/ or baking. Residual solvent is not 1 I left behind upon evaporation of the emulsionf A typica emulsion formula which is suitable is as follows:

Oleamide water emulsion Oleamide 10.00. Nacconal NRSF 3.00 (sodium salt of an alkylated naphthalen sulfonate); I

Water 87.00. Concentrated aqua ammonia 0.04. I Sodiumnitrite a 0.05. 1

To emphasize the unique lubricating? action which is I achieved in a very limited and selective class of lubricant modifiers, the following table illustrates lubricants which are not operative and which cause seizing, galling and of polymer suspended in water.

of the above characteristics are available commercially as by-products of low molecular weight recovered from commercial polymerizations. All of these materials are obtainable in aqueous emulsion containing conventional emulsifying agents, e.g., organic sulfonatesor non-ionic detergents and in varying concentrations up to about 35 The metal'blank coated as outlined above was formed into an L and the coating was tested by non-destructive apparatus called the Dermitron Non-Destructive Thickness Tester made by the Unit Process Assemblies, "Inc;

. The test disclosed that the straight blanks before forming scoring of the workpiece as aresult of lubricant failure and tearing away of the underlying encapsulating film and cold forming forces.

Unsatisfactory lubricants on chlorinated rubber capsule for 99 Us stainless steel, cold-forming by method of US. Patent No. 2,971,556.

EXAMPLE II This example illustrates application of low molecular weight polyethylene emulsion as lubricant coating to encapsulated tube blank using chlorinated rubber as in Example I. steel blank as inExample I and a top coating of polyethylene emulsion was applied after the base coating was dried. I

Following are examples of polyethylene emulsion which are obtainable from commercial sources and which are used successfully in accordance with the present invention.

Commercial polyethylene and polypropylene lubricant modifiers 7 Percent solids as used,

Emulsion: percent in water Mixed polyethylene propylene glycols of melting points 37-110 C. 10-20 Low molecular weight polyethylene,

molecular range 400-16,000, softening range 90-105 C. Atactic linear polypropylene of molecular Weight range 400-16,000 10-20 There also may be usedthe homologous polymer atactic linear polypropylene of molecular weight range 400-16,000 of the above table having a softening point;

range of above 37 C. and up to 110 C. Various'fractions of the polyethylene and polypropylene materials The base coating was made on a stainless had an encapsulating film coating thickness averaging 1 mil. These same blank pieces subsequently formed into 90 Ls tested out as having a residual encapsulating film thickness of 1 mil.- 7 l EXAMPLE m This example illustrates the use of solid encapsulating film of waxy polyethylene glycol solution as lubricant over chlorinated rubber capsule in the method of Example I. In this example an aqueous emulsion of a waxy ethylene glycol polymer of molecular weight 4000-6000 was used. This composition had a softening point within the preferred range, e.g., above 37 C. and below 110 C. Additional examples of polyalkylene glycols, of about the same molecular weight range, e.g., above 2500 and up to 6000 are:

Phenolic terminated polyalkylene glycols of melting points 37-1l0 C. such as:

' Tergitol XD Tergitol NP-40 Tergitol NP-35 The forming operation as set forth in Examples I and II was carried out. 7

A satisfactory bend was made equal to lube B in the drawings.

EXAMPLE IV This example illustrates the use of a copolymer of vinyl chloride, vinyl acetate and carboxylic acid, VMCH and shows that a satisfactory bendwas made using oleamide as the top layer bythe method of Example I.

' In the foregoing examples there have been illustrated suitable lubricant modifiers such as oleamide, mixed polyethylene polypropylene glycols of melting points 37-110" C.; phenolic terminated polyalkylene glycols of melting points 37-110 C. like Tergitol XD, Tergitol NP-40, Tergitol NP-35; low molecular weight polyethylene and polyethylene glycols of melting points 37-110 C.

Thefollowing lubricant modifiers are also suitable as the principal ingredient of the top coating deposited from either volatile organic solvent or water emulsion:

Chlorinated paraffin of metling point 37-110 C.

Eicosane I V Myristyl myristate Tallow trimethylene diamine Stearonitrile Polyethyleneglycol 600 dilaurate Dimethyl dihydrogenated tallow ammonium chloride Dimethyl hydrogenated tallow furfuryl ammonium chloride Methyl trihydrogenated tallow ammonium chloride 7 Ethoxylated hydrogenated stearamide of melting point 50-50, 30-70 or '70-30 mixture of cetyl alcohol and stearyl alcohol Upon comparing the successful lubricant modifiers set forth in the examples hereinabove and the unsuccessful lubricant modifiers which are also set. out above, a surprising contrast of the successful cold-forming operation will be seen employing the preferred and limited class of lubricant modifiers. Itwill be appreciated that the cold forming method and apparatus disclosed and claimed in copending application Serial No. 24,829 filed May 13, 1960, now abandoned and in US. Patent No. 2,971,556 granted February 14, 1961, serves as a testing system to determine the operativeness or inoperativeness of the lubricant modifier. In the instance that the lubricant is in the satisfactory category as disclosed herein a very low coefiicient of friction of the order of 0.01 to 0.02 in relation to the underlying encapsulating film against a polished steel die forming surface is achieved. This result is demonstrated by the fact that, as set forth in detail in Example I, cold-forming of the hard metal occurs without any change in thickness of the encapsulating coating or of the lubricant modifier and only the underlying metal suspended in the solid, hard substantially non-destructible encapsulating medium is caused to flow by the cold-forming forces which are in excess of the tensile and shear limits of the metal being formed.

It will, therefore, be appreciated that in this aspect of cold-forming utilizing the new and unexpectedly useful lubricants of the invention that the cold-forming apparatus employs a novel non-destructible encapsulating medium as a means to suspend the metal workpiece in a nonscoring relation to the metal of the cold-forming die and the lubricant modifier in tightly adhering relationship to the encapsulating medium effectively provides a new and positive apparatus means for successfully achieving cold forming under stresses beyond the elastic limit of the workpiece. The advantages in such apparatus apart from the precision of forming which the apparatus is capable of achieving lies also in the fact that heating of the metal is avoided, thereby preventing structural changes which are the rule rather than the exception in many of the hard alloy systems, for example in aluminum systems, iron systems, chromium systems, etc.

Having thus disclosed the invention, what is claimed is:

1. The method of reducing the coefficient of friction between opposed metal contacting surfaces of metal workpiece and die contacting each other under extreme lateral and normal forces to overcome the tendency to seize and gall comprising: encapsulating the workpiece in a hard, tough substantially incompressible synthetic plastic barrier material having an adhesion shear strength for said metal of at least about 600 pounds per square inch, a film tenacity of at least 3000 pounds per square inch, a Brinell hardness value of at least 20 and a high modulus of elasticity as evidenced by an elongation of at least about 3% up to about 15% before rupture, to isolate the rubbing metal surface of said workpiece from said die by the barrier consisting of said plastic material; treating the entire surface of said plastic with a lubricant having a melting point in the range of 37-110 C. and a coefficient of friction between said plastic barrier and steel of 0.01 to 0.02; cold-forming the plastic encapsulated and lubricanttreated workpiece in said die and thereafter removing the lubricant from said workpiece by treating with a solvent for the lubricant.

2. A method as claimed in claim 1 wherein said lubricant is a fatty nitrogen compound containing a long aliphatic carbon chain of from 12 to 24 carbon atoms attached to a single CN, Nil-I or NH group.

3. A method as claimed in claim 1 wherein said lubricant is a substance selected from the group consisting of fatty amides, fatty amines, fatty quaternary ammonium salts, a waxy ethylene glycol polymer of molecular weight 4000-6000, phenolic terminated polyalkylene glycol of molecular weight 2500-6000, mixed polyethylene-polypropylene glycols of molecular weight 4000-6000, atactic linear polypropylene of molecular weight range 400- 16,000, waxy polyethylene of molecular Weight range 400-16,000, mixtures of cetyl alcohol and stearyl alcohol, eicosane, tallow trimethylene diamine, stearanitrile, poly- 14 ethylene glycol 600 dilaurate, dimethyl di hydrogenated tallow ammonium chloride, dimethyl hydrogenated tallow furfuryl ammonium chloride, methyl tri hydrogenated tallow ammonium chloride, ethoxylated hydrogenated stearamide, ctdorinated parafiin and myristyl myristate.

4. A method as claimed in claim 3 wherein said plastic barrier is dissolved to remove it from said workpiece after said workpiece is formed by treating the resin material and lubricant thereon in an organic solvent which strips both the resin material and lubricant from the cold-formed workpiece.

5. A method as claimed in claim 4 wherein said plastic barrier is chlorinated rubber and said lubricant is oleic acid amide.

6. A method as claimed in claim 4 wherein said plasctic barrier is chlorinated rubber and said lubricant is polyethylene.

'7. A method as claimed in claim 4 wherein said plastic barrier is chlorinated rubber and said lubricant is polyethylene glycol.

8. A method as claimed in claim 4 wherein said plastic barrier is a material selected from the group consisting of chlorinated rubber, tripolymer of 87-95% vinyl chloride, 12-5% vinyl acetate and 0.5-2.5 of unsaturated carboxylic acid and copolymer of -85% vinyl chloride With 40-15% vinylidene chloride.

9. A method as claimed in claim 4 wherein the plastic barrier is chlorinated rubber and said lubricant is lauric I acid amide.

10. A method as claimed in claim 4 wherein said plastic barrier is chlorinated rubber and said lubricant is a waxy copolymer of ethylene glycol and propylene glycol of molecular weight 4000-6000.

11. A method as claimed in claim 4 wherein said plastic barrier is chlorinated rubber and said lubricant is waxy low-melting linear atactic polypropylene.

12. A method as claimed in claim 4 wherein said plastic barrier is the tripolymer of 87-95 vinyl chloride, 12-5% vinyl acetate and 05-25% of unsaturated carboxylic acid and said lubricant compound is oleic acid amide.

13. A method as claimed in claim 12 wherein said plastic barrier is modified with fusible, alcohol soluble, non-heat-hardening phenol formaldehyde resin, the amount of said modifier being up to 20% by weight of said polymer.

14. A method as claimed in claim 4 wherein the plastic barrier is copolymer of 60-85% vinyl chloride and 40- 15 vinylidene chloride and said lubricant is oleic acid amide.

15. A method as claimed in claim 14 wherein said plastic barrier is modified with a monor proportion of an amino resin selected from the group consisting of melamine formaldehyde and urea-formaldehyde, the amount of said amino resin being up to 20% by weight of said polymer.

References Cited by the Examiner UNITED STATES PATENTS Re. 24,765 1/60 White 29-149.5 2,331,547 10/43 Gessler et al. 117--75 2,333,922 11/43 Foster 117-75 X 2,349,951 5/44 Fuller et a1.

2,590,451 3/52 Perry.

2,866,774 12/58 Price 29-1495 2,971,556 2/61 Armstrong et al. 153-32 3,030,229 4/62 Esswein et a1. 11775 3,119,212 1/64 Esswein 117-75 WHITMORE A. WILTZ, Primary Examiner. HYLAND BIZOT, THOMAS H. EAGER, Examiners. 

1. THE METHOD OF REDUCING THE COEFFLICIENT OF FRICTION BETWEEN OPPOSED METAL-CONTACTING SURFACES OF METLA WORKPIECE AND DIE CONTACTING EACH OTHER UNDER EXTREME LATERAL AND NORMAL FORCES TO OVERCOME THE TENDENCY TO SEIZE AND GALL COMPRISING: ENCAPSULATING THE WORKPIECE IN A HARD, TOUGH SUBSTANTIALLY INCOMPRESSIBLE SYNTHETIC PLASTIC BARRIER MATERIAL HAVING AN ADHERSION SHEAR STRENGTH FOR SAID METAL OF AT LEAST ABOUT 600 POUNDS PER SQUARE INCH, A FILM TENACITY OF AT LEAST 3000 POUNDS PER SQUARE INCH, A BRINELL HARDNESS VALUE OF AT LEAST 20 AND A HIGH MODULUS OF ELASTICITY AS EVIDENCED BY AN ELONGATION OF AT LEAST ABOUT 3% UP TO ABOUT 15% BEFORE RUPTURE, TO ISOLATE THE RUBBING METAL SURFACE OF SAID WORKPIECE FROM SAID DIE BY THE BARRIER CONSISTING OF SAID PLASTIC MATERIAL; TREATING THE ENTIRE SURFACE OF SAID PLASTIC WITH A LUBRICANT HAVING A MELTING POINT IN THE RANGE OF 37-110*C. AND A COEFFICIENT OF FRICTION BETWEEN SAID PLASTIC BARRIER AND STEEL OF 0.01 TO 0.02; COLD-FORMING THE PLASTIC ENCAPSULATED AND LUBRICANTTREATED WORKPIECE IN SAID DIE AND THEREAFTER REMOVING THE LUBRICANT FROM SAID WORKPIECE BY TREATING WITH A SOLVENT FOR THE LUBRICANT. 